Electrical condenser



Nov. 20, 1923 1,474,486

1 B. MACPHERSON ELECTRI CAL CONDENSER Filegl June 5, 1919 14 Jill? IINVENTOR a9 a M @mn/Mwpiemv/V A TTORNEY Patented Nov. 20, 1923.

UNITED STATES PATENT OFFICE.

BYRON MACPHERSON, OF ROXBURY, MASSACHUSETTS, ASSIGNOR TO WIRELESS'SPECIALTY APPARATUS COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OFNEW YORK.

ELECTRICAL CONDENSER.

Application filed June 3,

which are set forth in the following specifi cation and accompanyingdrawing, which disclose the form of the invention which I nowconsider-to be the best of the various forms in which the principles ofthe invention may be embodied.

This invention relates to improvements in, electrical condensers of theplate or sheet type, especially of the type wherein the condenser isdivided into sections and the sec tions connected in series for highpotential service and the invention consists of certain improvements inthe condenser stack and the means for connecting the sections together.

Broadly the object of this invention is to provide an improved condenseradapted for iigh potential service.

In particular the object of the invention is to provide a connection orstrip between the sections of the condenser which insures a betterdistribution of potential between adjacent sections, which prevents anaccumulation of heat within the condenser and which allows readyinspection.

In the drawing Fig. 1 is a side elevation of the condenser with parts(the casing) in section.

Fig. 2 is an end elevation, the casing being omitted.

F 3 is an elevation on an enlarged scale showing the details ofconstruction of the condenser stack, the sections being separated orspread for inspection, and I.

Fig. 4 is an elevation similar to that of Fig. 3 and showing therelative position of the parts of the stack when clamped togeth- Thespace X shown around the stack K (Fig. 1) and its clamp A in the waxprotector or casing B is intended to illustrate the wax casing orcoating around the stack for the purpose of preventing brush dischargesand excluding moisture and air, and also preferably around the clamp.This is preferably a mass of wax cast in protector B as a mold andcompletely filling space X; but it is not necessary that the wax coatingcompletely fill space X, or surround clamp A and it may be 1919. SerialN0. 301,498.

no more than a thin or surface coating provided that it excludesmoisture and air from the interior of'the stack and assists 1npreventing brush discharges.

-In the type of condenser on which this invention is an improvement, thecondenser consists of a stack of plates or sheets, this stackbeingadapted for high potential service by being divided into sections whichare electrically connected together in series as will be more fullydescribed hereinafter.

The sheets, as usual, consist of successively located conductors andinsulators. In the present condenser such insulating and conductingsheets may be of any desired material but I use metal foil (as lead) forthe conducting sheets and mica for the insulating sheets and mycondenser is therefore known in the trade as a mica condenser, orspecifically, a high potential mica condenser for use in radiocommunication.

A desirable feature of such a condenser is a minimum volume but the highpotential developed makes this a difficult problem. The same is true inrespect of exposing a minimum of the conducting parts which are at highpotential. Other problems have arisen in connection with the importanceof the construction whereby the condenser stack is most desirably heldunder compression and kept permanently dry and free of air inside thestack and whereby brush. discharges are to be prevented.

In condensers of the type built up of series connected sections of equalcapacity the potential difference across the total condenser dividesequally across the several sections. If the several sections arearranged in a compact stack and the connections are of the usual type inwhich the terminals'or ends of the sections are alternately connected inpairs, a potential difference of twice that be tween the ends of asection exists between adjacent connections and between unconnectedadjacent ends of adjacent sections. This results in a brush dischargebetween said unconnected ends and between said connections unless alarge quantity of insulation is provided between'them. I have provided asystem of connection between adjacent sections for limiting thedifference of potential Jetween the adjacent ends of adjacent sectionsto a value equal to the potential difference between the ends of any onesection.

In condensers of the ty e carrying a heavy v load, as condenser ossesincrease markedly with increase in temperature, I have provided meanshereinafter described and constituting a feature of the presentinvention to cause radiation and COIldllCtlOIrOf heat from the condenserand especially from the interior of the condenser.

Another difficulty encountered in condensers of the types now in use isthat if one section breaks down either the whole condenser is rendereduseless or at least the adjacent sections. Furthermore with such priorconstructions it is very difficult to properly inspect the same and tomake replacements. For instance, in removing bad sections the othersections are often spoiled.

Another defect in construction now in use resides in the fact thatmistakes in connecting the sections, short circuiting the sections, arecommon.

These various-problems have been solved and such defects overcome in apractical manner by this invention wherein the construction has beendeveloped around my conception of connecting the sections of the stackin series, and particularly in connection with the arrangement for theconnection of the sections as more clearly shown i Figs. 3 and 4.

In the embodiment of the invention here illustrated the terminals atopposite ends of the stack are of opposite potential, one low and onehigh, but the invention is applicable to other arrangements. One end ofthe stack is connected to a high potential terminal H P T, the oppositeend of the stack being connected to a low potential terminal L P T. Theexpressions high potential terminal and low potential terminal are, ofcourse, only relative terms and the actual high and low potential pointsdepend entirely upon the condition of the circuit in which the condensermay be used. As illustrated in Fi s. 1 and 2 the high potential terminalH I T is connected by lead 4 to one end of the stack K, the terminal H PT being itself mounted in the insulating cover C. The low potentialterminal L P T may be the metal part of the cover M C (Fig. 1) or theWax protector B if that be of metal. In any case terminal L P T may beconnected by lead 5 with the section S at the opposite end of the stack.The specific high potential terminal is merely illustrated and describedfor the purpose of showing the application of the stack to the casingand constitutes no part of the present invention. The specific casingand terminal is more full shown and described in an application ofreenleaf Whittier Pickard Serial Number 292,126, filed April 23, 1919.

The particular condenser here illustrated and described as an embodimentof the invention is a type of a standard capacity 0.004 micro-faradcondenser in extensive use I with transmltters 1n radio communication.

In this form each section S consists of the size, number and thicknessof sheets which will give the condenser a capacity of 0.004 micro-faradaltho it is to be understood that the stack may have any desirablecapacity and comprise any number of sections and still be within thescope of this invention.

Of course, the stack K of this condenser, like any condenser stack ofsheets, requires initial treatment during manufacture for the purpose ofremovinginternal air and moisture and consolidating the stack of sheetsbefore being covered with the coat-in of wax X, (Fig. 1) whichthereafter is to eep out the air and moisture. Any of the various wellknown methods may be used for this treatment which usually includesimmersion in molten wax, in or out of vacuo, and a compression orvariation of the compression of the stack. For this purpose the sectionsare maintained in clamping position by any suitable clamp preferablythat which accompanies the stack and maintains it in clamping position.

The stack and the clamp as in Fig. 2 are assumed to have been properlytreated as above, and in pro-per condition of clamping pressure and areready to be surrounded by their casing of wax The wax protector B is socalled because it may serve initially as a mold for the wax casing Xwhen the latter fills container B, yet thereafter protector B remains asa permanent part of the assembly for the purpose of protecting the waxcasing which it does whether the casing be merely a coating around thestack K or a thick mass entirely filling protector B.

In preparation for the casting of the wax in receptacle B the stack Kand clamp A in place around it are inserted in receptacle B as the. moldand protector and secured therein in any suitable manner.

The wax protector B may be of any desired material or shape because ithas no necessary mechanical or electrical E:ooperation with thecondenser stack. Thus it may consist of any simple wood or fiber box ofany size or shape if desired. In fact as the stack K and clamp A.constitute the complete operative condenser, they may be used withoutcasing or coating of wax, but, of course, it isextremely advantageous toprovide a wax protector and also to have it of metal as the mostpractical form of condenser. I prefer that the wax protector B be ofmetal as aluminum as a simple and economical construction. Aluminumislight and cheap and easily shaped. but any other metal may be used, suchas tin.

At the time that the stack and clamp are cast in B the high potentiallead and the low potential lead are left projecting above the wax, inpreparation for the application of the condenser cover.

After the wax in protector B has been cooled and solidified, the'top orcover may be applied upon asket G interposed for water tightness. he lowpotential lead .5 may be laid either over or under the gasket G. Thenthe cover and protector B are secured together as in Fig. 1 to completethe assembly.

I The low potential lead 5 may be a ceo(pper strip the upper end ofwhich is pinch between metal cover M C and the flange 2 of metal casingB and the lower end of which is secured to one end of the lowermostsection.

The cover may have the construction shown because it plays no part incompressing the stack, a comilete and independent clamp A. bein provi edfor the stack. The central part 5 is of cheap insulating material suchas electrose or the like, molded as shown about the anchors H (Fig. 1)which project radially inward from the metal part M C of the cover. Thecentral insulating part C of the over is molded with an upper hole andlower recess shown for the reception of the terminal H P T and itsassociate parts. If desired the entire cover may be of insulatingmaterial.

Before the cover is applied, the high potential lead 4 left projectingup above the wax casing X is connected up thru gasket G to the terminalH P T. The means for making such connection is designed to ob- -viatethe necessity of using a long lead.

This terminal consists of a piece of square brass stock 6 which fits inthe s uare hole 7 shown in molded cover G. The upper end of the terminalH P T projecting above cover C is turned to be round and is threaded toreceive nuts 8 and 9. The lower end of this terminal is tapped toreceive a screw 10. Before cover C is put in place, lead 4, (of copperbraid or strip) projecting above the wax casing X which is flush withthe top of receptacle B, is soldered to a In or connector 11. At thistime terminal H T is not in place in the cover. The screw 10 is then putthru a washer 12, then thru lug 11 and then a. gasket 13 is placed ontop of lug 11. Next screw 10 is screwed into the tapped hole 14 in thebottom of terminal H l T, the latter then being pushed up thru the suare hole in the cover. The metal part C of the cover is fastened inplace over gasket G by screws 15; Then lower nut 8 is applied to the topof terminal H P T to draw it up tight, which compresses gasket 13between lug 11 and the top of the recess in the cover, thereby sealingthe terminal against ingress of moisture. Upper nut 9 is for clampingany desired connection to H P T.

Figs. 3 and 1 show (with my improvements in detail) the stack dividedinto sections S b them and connectin the sections in series to adapt thestack Tor high potential service. Here, as heretofore, each section Scomprises a plurality of alternately disposed sheets of mica and foil,the mica being of larger area than the foil sheets. For the sake ofclearness the correct proportion of the parts are not shown in Figs. 3and 4.

Each pair of adjacent sections are separated from each other by twoinsulating sheets or separators 1 which may be of mica and which areinterposed between such sections and upon opposite sides of a conduct;ing sheet or connector 16 which may be of any suitable material which isa ready conductor of electricity and heat, as, for inplacing insulatingsheets between stance, copper, and which extends'between the sectionsparallel therewith. These conducting sheets have preferably asubstantial tensile strength at least greater than that of the lead ortin foil constituting the parts of each section and also someflexibility. From each end of each section S there extends a bunch 17 offoil in that section, in order to permit the sections to be connectedtogether. These bunches of foil are fragile and easily torn and brokenespecially when covered with hard wax, and heretofore it has been foundthat in assembling the sections it oftentimes happens that the condenserwas damaged so that it could not be used. At least great care had to beexercised in assembling the same. This difii culty is obviated 'byconnecting the bunch 17 at a given end of one section S with the bunchat the opposite end of an adjacent section S preferably by means of theconnectin sheet 16. One end 18 of sheet 16 is double back around thefoil bunch at one end of a sect-ion and around the adjacent end of aninsulator 1 in the manner shown in Fig. 3 and soldered to the remote orouter side of the bunch as indicated at 19.

The opposite end 20 of connector 16 is similarly folded around the foilbunch at the opposite end of the adjacent section and around theadjacent insulator 1 and soldered to the outer or remote portion of thatbunch and so on thru the stack, connecting all the sections S togetherin series.

It should be noticed, referring to Figs. 3 and 4 that the portion of theconnecting strips 16 adjacent to the inner portions of the foil bunchesare unattached thereto, thereby allowing play and a large degree offlexibility. By the present construction, the sheets 1 can be arrangedsymmetrically between the sections and upon opposite sides of theconducting sheets 16, so that their ends project equal distances fromopposite ends of the sections but not beyond the extreme outer portionsof the connections 16 sections, connectors and separators together holdsthe parts in close contact under pressure independently of the cover.This clamp comprises a metallic block or base plate 21 on which stack Krests. This base plate may be of any suitable material and .s secured inany suitable manner to the bottom of the casing. To the top of the stackis applied a pressure block or plate 22 having an upper convex surface23. A flexible loop or band 24 of insulating material preferably offiber such as fish paper, which is very durable and does not stretch,connects the blocks 21 and 22 to clamp the same against the ends of thestack. This loop preferably comprises several layers or plies of suchfish paper. The intermedlate portion 25 extends over the block 22engaging the convex surface thereof and the closed ends 26 of the loopextend on opposite sides of the stack and are connected to parallelclamping bars 27 upon the base plate on opposite sides of the stack K,the closed ends of the loop extending below the bars 27 and the barsbeing interposed between the plies of the loop. These clamping bars 27are fastened or connected to the base plate 21 by means of screws 28extending thru the base plate and threaded thru holes 29 in the bars. Byadjusting the screws the loop 24 is drawn upon pressure block 22 tightlyclamping the parts of the stack together between the blocks. The band24: is of substantial width, the sides facing the opposite sides of theseveral sections of the stack K, and constitute an insulating barrierbetween the stack and the adjacent walls of the casing B, the clamp ofcourse being imbedded in wax. The fish paper band is preferably treatedwith armalac to prevent it from being affected by the hot wax and heatand to cause it to better stand the strain placed upon it. Inassembling, the stack is preheated and the clamp tightened while thestack is under pressure. The clamping bars 27 are well outside thevoltage gradient line and as the fiber is a fine non-conductor the twoends of the stack are carefully insulated from each other and the stackclamped. It is to be understood, however, that the present invention canbe used with any suitable form of clamp, altho I have not abandoned theinvention embodied in the clamp herein illustrated and described.

By connecting the sheets as above describe a much neater stack isprovided and the soldering is better. The construction provides anaccordion like arrangement wherein the sections may be easily separatedand the bad sections taken out and repaired without harming the otherparts of the stack. Furthermore, the metal conducting sheets 16 betweenthe sections are of substantial width, thereby acting as a shield orguard between sections protecting perfect sections against damage due toimperfect or injured sections adjacent thereto.

The connection 16 also provides means for conducting heat from thecenter of the stack to the exterior thereof. The ends of the connectingsheet 16 extend a substantial distance into wax X and are imbeddedtherein to conduct heat from the interior of the stack to the outside,the adjacent ends being maintained in separated relation to each other.

Another advantage of the zigzag or accordion construction for connectingthe sections together lies in the fact that the soldering of thesections together can be done in one half the time formerly requiredsince when forming the stack it will be necessary to solder on one sideonly. The method of constructing the present stack as follows: One endof each connecting sheet 16 is bent over or around the foil bunch at oneend of a section and soldered thereto, the heat being applied to theoutside of the sheet to prevent damage to the foil bunch. The sectionsare next stacked with the connecting strips 16 interposed between themand with their free ends all lying at one side. The sections andconnecting sheets 16 are properly supported in a clamp and the free endsof the connecting strips are bent over or around the bunches at theopposite ends of the sections and soldered thereto as above described.In this construction there will be no bending of the foil ends orbunches which are often damaged by such bending because such movement isvery apt to break off the foil especially when covered or stifi'enedwith hard wax, the flexible connectors 16 maintaining and supporting thebunches in position. By providing such strips or connectors which extendaround the foil bunches and to one side. a substantial surface isprovided for applying a hot iron without danger of breaking off the foilas now often happens in assem ling the sections. In assembling thesections in the zigzag or accordion method, the end connectors 4 and 5leading from the end sections to the terminals will always come off atthe proper place to wit, opposite ends of the sections, regardless ofthe number of sections. I provide a simple and symmetrical stack whichmay be easily and quickly assembled with danger of faulty connection at.1 minimum.

In the present construction, one section can be removed without spoilingthe others, as the strips or connectors 16 are flexible and take up allmechanical strains and can be removed by merely heating the surface ofthe sheets with a hot iron. The stack furthermore can easily beinspected because the sections can be separated like an accordion.

By bending the ends of the connectin sheets 16 in opposite directionsand \roun opposite ends or bunches of adjacent sections and solderingsaid free ends to the remote or outer portions of the foil bunches withthe inner portions of the bunches and adjacent portions of theconnectingsheet unattached, permits the ends of the foil bunches to besoldered'without bending the foil bunches toward one another, whichbending has resulted in the past in a considerable tension strain onthe-foil sheets on the side of the direction of bending and acompression or crumpling strain on the other side of the foil sheets,which has resulted in tearin the foil from the sections as mentioned aove, all of, which resulted in sparking and consequent destruction ofthe stack when put into use.

By means of the present invention, the foil bunches of each section arepermitted to stand straight out when electrically assembled so that thefoil bunches are under no excessive strains. The bent or doubledportions of the outer ends 18 and 20 of the sheets lfi'permit each suchportion to bridge over one end of an insulating sheet 1 so that allinsulating sheets can be substantially of the same length .and projectequal distances beyond theends of the sections but not beyond theconnectors.

The present construction has an important electrical advantage overprior condensers wherein the sections are connected n by means of adifferent arrangement consisting of connecting the terminals or ends ofthe sections alternately in pairs. It would increase the cost ofproduction in this arran ement to exercise such care so toinsure t atthe sections be properly connected in the stack, but also said-priorarrangement resulted in providing a. potential difference across theunconnected adjacent ends-of adjacent sections and adjacent con nectors(and consequent strain on the insulating sheets between the sections)which was twice'that between the two ends of a section. =The result waseither a tendency to breakdown the insulation or at least cause brushdischarges from the opposing sheets. These defects are avoided in myarrangement wherein the potential difference between an end of acondenser section S and anadjacent end of the adjacent section can neverexceed the potential difference between the ends of a single-section andwherein there is no harmful action due to potential difl'erences betweenopposing faces between the sections and sheet 16 at any point thanthe'total potential difference between the two. ends of such section.and the same applies "to the relation between as an electrical barrierbetween the oposing faces of adjacent sections in the sense thateven ifthere be considerable difference of potential between opposing faces ofadjacent sections, yet sheet 16 acts to divide such potential differencebecause it is kept at an intermediate potential by reason of the factthat its ends are connected to opposite or remote terminals of the samesections which its, body separates. These terminals must therefore be atthe same potential and the difference of potential between any suchterminal and an adjacent terminal of an adjacent section can be nogreater than the difference of potential between the ends of eitheradjacent section. From this it will be apparent that the insulatingsheets 1 have the function of insulating conducting sheet 16 fromad'acent sections altho they will not have to wlthstand a greaterdifference of potential than that between the ends of a given section.

The arrangement of Figs. 3 and 4 has further advantages which are usefulin manufacturing. Thus, in makingthe'stack all the sections areconnected together mechanically in the zigzag arrangement (besire stepsin the treatment, testing, etc.

The metal of connecting sheets 16 takes up the strainsaccompanying saidaccordion ac-' UOIIYSO that there is no undue strain on the solderedjoints, altho of course it is desirable 'to have a joint of considerablearea between connectors 16 and thefoil bunches.

I claim f 1. A high potential condenser consisting of a stack ofsections adapted to be con nected together in series, and a metal sheetbetween adjacent sections connected at one end to a given end of one ofsaid adjacent sections and connected at its other end to the oppositeend of the other of said adjacent sections whereby said sections areelectrically connected in series.

2.-A high potential condenser consisting of a stack of condensersections, from which project bunches of the conducting sheets forconnection together in series; two sheets of insulating material betweeneach pair of adjacent sections, and a metal sheet located between saidinsulating sheets-and formed with inwardly directed ends which extendfrom theirintegral metal sheet in opposite directions from each otherand are electrically connected with the adjacent bunches of conductinsheets.

3. A high potentia series condenser consisting'of a stack of sectionsfrom which project bunches of the conductin sheets for connection ofthe'sections together; and a metal. sheet located between adjacentsections and being electrically connected 'at one end to the foil bunchprojecting from a given end of one of said adjacent sections andelectrically connected at its other end to the foil bunch projectingfrom the opposite end of the other of said adjacent sections.

4. A high otential condenser consisting of a stack 0 sections from whichproject bunche of conducting sheets for connection of the sectionstogether in series and a metal sheet between adjacent sections havingone end extending around and connected to the outer portion of the bunchat a given end of one of said adjacent sections and having its other endextending around and connected to the outer portion of the bunch at theopposite end of the other of said adjacent sections.

5. A high potential condenser consisting of a stack of sections adaptedto be connected together in series, and a flexible sheet betweenadjacent sections connected at one end to a given end of one of saidadjacent sections and connected at its other end to the opposite end ofthe other of. said adjacent sections, to allow an accordion likeseparation of said sections.

6. A high potential condenser consisting of a stack of sections adaptedto be conneeted together in series, a metal sheet between adjacentsections connected at one end to a given end of one of said adjacentsections and connected at its other end to the opposite end of the otherof said adjacent sections and electrically connecting said sec tion inseries, and sheets of insulating material between-said adjacent sectionsand upon opposite sides of said connecting sheet.

7. A high potential condenser consisting of a stack of sections adaptedto be connected together in series, a metal sheet between adjacentsections connected at one end to a given end of one of said adjacentsections and connected at its other end to the opposite end of the otherof said adjacent sections, and sheets of insulating material interposedbetween said adjacent sections upon opposite sides of said connectingsheet, said insulating sheets being syn'imetric-ally arranged in thestack and projecting substantially equal distances from opposite sidesthereof to points inwardly of the ends of said connecting sheet.

8. A high otential condenser consisting of a stack 0 sections from whichproject bunches of conducting material for connection of the sectionstogether in series, and a metal sheet between adjacent sections havmgends extending in opposite directions around and secured to the outerportions of bunches at oppositeends of said adjacent sections and beinunattached to the inner portions of said unches whereby the severalsections are flexibly connected together and can be convenientlyseparated for inspection.

9. A high potential condenser consisting of a stack of sections adaptedto be connected together in series, and a metal sheet/between'adjacentsections electrically and mechanically connected at one end to a givenend of one of said adjacent sections and electrically and mechanicallyconnected at its other end to'the opposite end ofthe other of saidadjacent sections, insulating sheets between said adjacent sections andupon opposite sides of said'connecting sheet and means for clamping theseveral sections and sheets together. s

10. A high potential condenser consisting of a stack of sectionsconnected in series, dividing the total potential of the condenser amongthem and comprising a sheet of conductive material interposed betweenadjacent sections for. conducting heat from the interior of the stackand to serve as a protective guard between the sections.

11. A high potential condenser consisting of a stack of sectionsconnected in series,

dividing the total potential of the condenser among them and comprisinga sheet of conductive material interposed between adjacent sections forconducting heat from the interior of the stack and to serve as aprotective guard between the sections and sheets of insulating materialinterposed between each side of said conductive sheet and an adjacentsection.

12. A condenser consisting of a stack of sections adapted to beconnected togetherelectrically, and a metal sheet interposed betweenadjacent sections, extending beyond the bodies of said sections andconnected thereto whereby said sheet performs the dual function ofelectrically and mechanically connecting said sections and providingheat conducting means to conduct heat 1 lating means interposed betweensaid sections upon opposite sides of said connecting sheet and a waxlike substance in said casing in which said several sectionsandconnecting sheet with projecting ends are imbedded.

14. A condenser consisting of a stack ofsaid sectlon and said metalsheet.-

15. A high potential condenser consisting of a, stack of sectionsarranged in series, dividing the total potential of the condenser amongthem and from which project bunches of conductin sheets, a flexiblemetal sheet having relatively greater tensile strength than the materialof which said bunches are composed, interposed between adjacentsections, having one end bent around a bunch at one end of said adjacentsection and secured to the outer portion thereof,'and having itsopposite end bent around the bunch at the opposite end of the other ofsaid adj acent sections and secured to the outer portions thereof, andbeing unattached to said bunches on theirinner portions, insulatingsheets interposed between adjacent sections upon opposite sides of saidconnecting sheet and arranged symmetrically in the stack and clampingmeans for said stack.

16. In a condenser, a. stack comprising a plurality of sections havingfoil terminals, and means for electrically connecting said sections,comprising a sheet of metal intered between the sections and projectingyond the same, and to the projecting por-' tion of which and by whichthe foil terminals are connected and supported respectively.

17. In a condenser, a stack of sections of alternate sheets ofdielectric and relatively fragile foil, and means electricallyconnecting the sections together, including heat-conducting sheets of.metal of relatively greater tensile strength than said foilandinterposed between sections and extending beyond the same.

18. In acondenser, a stack of sections comprisin alternate sheets ofrelatively fragile foil and dielectric, electrically conneeted andcomprising sheets of conductive material having relatively greatertensile strength than said foil, and interposed between sections forconducting heat from the interior of the stack and to serve as a guardbetween sections.

19. In a condenser, a stack comprising a plurality of sections, meanselectrically connecting said sections comprising a metal sheetinterposed between sections, and sheets of insulation interposed betweeneach side of said metal sheet and an adjacent section.

20. In a condenser, a stack of sections composed of alternate sheets ofdielectric and relatively fragile foil and electrically connected, ametal sheet of relatively greater tensile strength than said foilinterposed between said sections, and clamping means for the stack.

21. In a condenser, a stack of sections com posed of alternate sheets ofdielectric and relatively fra 'le foil having foil terminals andelectrical y connected together, and a metal sheet of relatively greatertensile strength than said foil interposed between and projecting beyondsaid sections and supportin saidfoil terminals.

22. n a condenser, a stack of sections made up of alternate sheets ofdielectric and relatively fragile foil having foil terminals, meanselectrically connecting said sections comprising heat-conductin sheetsof metal of relatively greater tensfie strength than said foil,interposed between and extending beyond the sections, and to theextending portions of which and by which the foil terminals areelectrically connected and supported respectively, a clamp for saidstack, and a metal casing for said clamp and stack, and constituting oneterminal of the condenser.

BYRON MACPHERSON.

